On Mon, 8 Feb 2021 at 20:07, Kaneda, Erik [off-list ref] wrote:

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-----Original Message-----
From: Rafael J. Wysocki <rafael@kernel.org>
Sent: Monday, February 8, 2021 5:01 AM
To: Shawn Guo <redacted>; Ard Biesheuvel
[off-list ref]; Kaneda, Erik [off-list ref]
Cc: Linux ARM <redacted>; ACPI Devel Maling
List [off-list ref]; Linux Kernel Mailing List <linux-
kernel@vger.kernel.org>; open list:ACPI COMPONENT ARCHITECTURE
(ACPICA) [off-list ref]; Wysocki, Rafael J
[off-list ref]; Len Brown [off-list ref]; Moore,
Robert [off-list ref]
Subject: Re: [PATCH] Revert "ACPICA: Interpreter: fix memory leak by using
existing buffer"

On Sat, Feb 6, 2021 at 11:49 AM Shawn Guo [off-list ref] wrote:

quoted

On Sat, Feb 06, 2021 at 09:49:37AM +0100, Ard Biesheuvel wrote:

quoted

This reverts commit 32cf1a12cad43358e47dac8014379c2f33dfbed4.

Hi Bob, Ard and Rafael,

quoted

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The 'exisitng buffer' in this case is the firmware provided table, and
we should not modify that in place. This fixes a crash on arm64 with
initrd table overrides, in which case the DSDT is not mapped with
read/write permissions.

Since this code runs on basically every _HID and _CID invocation, I would have expected this kind of revert to come in for kernels that do not use initrd override... So it sounds like there is a difference between how pages are mapped for initrd table overrides and tables exposed through the XSDT for ARM.. I think it would be easier for us to make these fixes in the future if we could all come to a consensus on whether if we should assume that these pages are writable or not.

Should we assume that all ACPI tables are non-writable and read only regardless of initrd override and architecture?

ACPI tables are measured into the TPM on measured boot systems, and
checksummed, so I don't think we should ever modify them in place.

But if we need code like this, it should be conditional at the very
least, i.e., it should only rewrite _HIDs and _CIDs if they are
incorrect to begin with.

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